The present invention is related to clock synthesizing, and in particular to calibration of voltage controlled oscillators.
Electronic circuits often use clock signals to regulate and control their operation. Events in the electronic circuits are timed by rising and/or falling edges of the clock signals. Clock signals may be generated by a number of oscillating circuits, such as an LC voltage controlled oscillator (VCO). In this type of oscillating circuit, an electrical charge is alternately accumulated and discharged to form the basis of the clock signal. The charge accumulates in inductors and capacitors of an LC tank circuit in the VCO, and the time needed for the charge to accumulate and discharge is based on the inductance and capacitance values. The frequency of the clock signal in one exemplary VCO may thus be controlled by varying the capacitance of the LC tank circuit in the VCO. For example, the VCO may include a voltage controlled variable capacitor so that the voltage of a control signal may be used to control the output frequency.
It is often desirable for a VCO to have a wide tuning range so that the VCO may be tuned to produce any of a wide range of output frequencies. The gain of the VCO may be increased so that is more sensitive to the voltage of the control signal, allowing the input voltage to select a wider range of capacitance values in the VCO and produce a wider range of output frequencies. However, increasing the gain of the VCO also makes it more susceptible to electrical noise on the control signal. A very sensitive VCO may have difficulties locking onto a reference frequency, because noise on the control signal can make the output frequency of the VCO fluctuate too greatly.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced VCOs.